In the case of when alkene, in particular, ethylene is subjected to the copolymerization in conjunction with an alkyl(meth)acrylate comonomer, a polymer that has physical properties different from those of typical polyethylene may be formed. For example, the adhesion strength, properties such as the low temperature toughness and the like may be significantly improved as the content of comonomer(s) is increased. Accordingly, the much development of the copolymer including 1-alkene and the other comonomers mixed with each other has been made.
In a related art, the copolymer of ethylene and alkyl acrylate or ethylene and alkyl methacrylate is obtained by using the high temperature and high pressure reaction. Thus, the reaction by simultaneously adding ethylene and an acryl monomer by using a tube type of reactor or an autoclave reactor under the severe condition of 1000 atm or more and 100° C. or more is disclosed. The polymer that is obtained under this condition is a copolymer polymerized by using the acryl monomer that is the polar monomer in an amount of 3 to 35% based on ethylene.
However, in order to ensure the high temperature and high pressure condition, an additional apparatus such as a primary compressor, a secondary compressor, and a special reactor is required to ensure safety of operators. In addition, due to the severe process condition, there are many condition limits when the composition of the copolymer is to be changed in a desired direction.
In addition, the ethylene copolymer that is manufactured by using a known method includes few polar groups. That is, since the content of polar monomer is not high, the crystallinity of polyethylene remains in the copolymer. Thus, there is a limit in use of the copolymer in an optical material such as a transparent film. Accordingly, in respects to the polymer that is obtained according to the known high temperature and high pressure method by using tube type of reactor or autoclave, products that do not affect the transparency have been mainly developed.
Accordingly, there is a need to develop a novel method of manufacturing a polar copolymer that has no crystallinity due to the high content of polar comonomer without the high temperature and high pressure severe polymerization condition.
Meanwhile, a method of copolymerizing vinyl monomers in olefin by using a metal complex compound catalyst is known. However, due to the high affinity in respects to oxygen of the metal, the metal complex compound catalyst on the basis of an initial transition metal and a lanthanide metal is disadvantageous in that the catalyst is easily contaminated by a functional group (C═O) of the polar vinyl monomer. In respects to a metal complex compound catalyst system on the basis of a latter transition metal, the high possibility of the copolymerization of alkyl acrylate and olefin is reported, but the content of olefin is still very high.
In order to overcome the disadvantage of the metal complex compound catalyst polymerization method in which the metal complex compound catalyst is contaminated due to oxygen that is present in the polar group, thus reducing the activity and forming a polymer having the low content of polar groups, the controlled radical polymerization has been suggested. In the case of when olefin and the polar vinyl monomers are subjected to the copolymerization by using the ATRP (Atom Transfer Radical Polymerization) that is the representative method of the controlled radical polymerization, the content of the polar vinyl monomer is higher than the content of olefin unlike the metal complex compound catalyst polymerization. That is, it is possible to synthesize a random copolymer in which the content of olefin is appropriately controlled according to the polymerization condition. However, in the case of when the ATRP is used, a long time is required to obtain the high molecular weight, and there is a limit in maintaining the content of olefin at a low level. Since the 1-alkene-acrylate copolymer has the high transparency, the copolymer is usefully applied to an optical material. However, in order to use the copolymer for the above purpose, the excellent heat resistance must be ensured so as to prevent deformation due to heat generated during the manufacturing process and the operation of optical apparatuses. Accordingly, there is a need to develop a novel copolymer in order to improve the physical properties such as the heat resistance and the like.